Typically, franking machines comprise franking means making it possible to apply a franking mark to a item of mall.
Means for control and management of these franking means make it possible to calculate the franking value and to create the mark applied to the item of mail.
Such machines also comprise means for accounting for the franking operations. Generally, they comprise a so-called ascending register, of which the value is increased, each time a franking mark is printed, by the amount of the value of that franking operation, and/or a so-called descending register, of which the value is decreased by that same franking value.
The so-called ascending register thus represents the total value of the franks printed by the machine since it was put into service whereas the so-called descending register indicates the available credit not yet used up since the last re-crediting of the machine in monetary units.
For the operation of such machines, it is necessary to re-credit the so-called descending register periodically. It is moreover useful to make readings of the registers or produce various statistics on the franking operations performed by the machine.
Systems are known which enable re-crediting information to be transmitted to a franking machine, by virtue of a memory card of chip card type, which is transported between the computerized control center and the franking machine. Such a system is described for example in the patent application FR 94 10530 in the name of the present applicant.
However, to obtain a register re-crediting instruction, the user must make a request to the control center, which creates the card storing the re-crediting instructions and then sends it to the user.
Such a system has the drawback of being long to implement as well as using a card which passes between the center and the site on which the franking machine is used.
In order to speed up the re-crediting operation, a data communications terminal can be used on the user's site, this terminal being linked to the control center by means of a modem, the communication passing via the public telephone network. Each memory card, respectively associated with a franking machine, may be inserted in the terminal, and re-crediting data, sent by the center, are written on the memory card. This card is next installed in conventional manner in the associated franking machine.
However, even in this improved system, the memory card is periodically extracted from the franking machine. It must consequently have significant guarantees for avoiding any fraud on the data written on that card.